Blade holding mechanism for coaters



Dec. 26, 1967 c, REMPEL ET AL 3,359,940

BLADE HOLDING MECHANISM FOR COATERS Filed sept. 17, 1965 5 sheets-sheet 1 NVENTR.

@AQ ATTORNEYS Dec, 26, 1967 I C, REMPEL ET AL 3,359,940

BLADE HOLDING MECHANISM FOR COATERSl Filed sept. 17, 1965 5 sheets-sheet 2 INVENTOR.

m mM/Za A-TTORNEYS C. REM PEL ET AL BLADEv HOLDING MECHANISM FOR coATERs Dec. 26V, 1967 3 Sheets-Sheet 3 Filed Sept. 17, 1965 INVENTOR. COQ/Q05 Qin/,QQ /QQ/z/OQ M65/,Mfr

m ATTORNEYS United States Patent 3,359,940 BLADE HOLDING MECHANISM FOR COATERS Cornelius Rempel and Arnold J. Schmitt, Beloit, Wis.,

assignors to Beloit Corporation, Beloit, Wis., a corporation of Wisconsin Filed Sept. 17, 1965, Ser. No. 488,090 15 Claims. (Cl. 118-126) ABSTRACT OF THE DISCLOSURE Doctor and clamping mechanism for the doctor bla-de of trailing blade coaters. The doctor blade is supported on a machined holding plate mounted on the front face of the doctor back and is clamped to the holding plate by a clamping plate carried by a series of pivoted clamping arms. An inflatable tube between the clamping arms and the clamping plate maintains a uniform pressure across the clamping plate and doctor blade. The pivot for the clamping arms is spaced far enough away from the machined surface of the clamping plate, to enable separation and ready access to the holding and clamping plates, for cleaning. A positioning mechanism enables the ang-le of the doctor blade to be changed as required. This includes a stop for the doctor back and doctor blade which is carried by the main bearing support for the back-up roll. This maintains the stop in the same position relative to the back-up roll, regardless of the angle of adjustment of the doctor blade with respect to the back-up roll.

Summary of the invention and objects This invention relates to improvements in doctor backs for coaters for coating traveling webs of paper and more particularly relates to an improved form of blade holder for holding the doctor blade to the doctor back.

The present invention has as its principal objects to provide an improved form of blade holder for holding a doctor blade to a doctor back arranged with a view toward maintaining a uniform clamping pressure on the doctor 'blade throughout the length thereof.

Another object of the invention is to provide a novel form of doctor blade holding mechanism for holding the doctor blade to the doctor back of a web coater, such as is used in the coating of paper and the like, so constructed and arranged as to provide uniform clamping pressure on the doctor blade throughout the length thereof and to widely separate the clamping means from the doctor blade and accommodate ready cleaning of the blade and clamping or holding mechanism, and thereby avoid the nonuniformity of the clamping surfaces caused by the drying up' of coating on the clamping surfaces.

Still another object of the invention is to provide a simplified form of blade clamping or holding mechanism for clamping doctor blades to doctor backs of coaters and the like, in which the clamping surfaces are so arranged as to insure a trued doctor blade even though the clamping parts may war-p. p

A still further object of the invention is to improve upon the holding mechanisms for holding doctor blades to doctor backs by pivotally mounting the blade clamping members on the doctor back with the pivots thereof spaced a substantial distance from the doctor blade t0 increase the clamping leverage and enable Wide separation of the clamping members for ready wash up of the doctor blade and clamping members.

A still further object of the invention is to improve upon the holding mechanisms for doctor -blades formerly in use by clamping the doctor blade to the doctor back by a pivotally movable clamping bar retained in clamping engagement with the doctor blade by power, and by ICC . an improved clamping means for clamping a doctor blade to a doctor back, utilizing two accurately machined plates, one serving as `a supporting plate for the doctor blade and the other serving as the clamping plate for the blade and having a machined t therewith and supported on a series of pivoted clamping arms pivoted to the doctor back in spaced relation with respect to the clamping plate, to assure wide separation of the plates and moved by fluid pressure means to open and close the clamping means and to maintain the clamping means in clamped relation with respect to each other.

Still another object of the invention is to provide a clamping means for clampinga doctor blade to a doctor back utilizing a support plate extending the length of the doctor back and secured thereto and clamping the doctor blade to the doctor back by a clamping plate extending for the length of the doctor blade and movably mounted on a series of spaced clamping arms pivoted to the doctor back and moving the clamping plate into clamping engagement with the support plate by power, in which a back-up bar backs up the clamping plate and is mounted on the clamping arms and -has an expansible pressure member extending for the length thereof maintaining uniform pressure on the clamping plate througout the length thereof and thereby holding the doctor blade in alignment, even though the back-up bar may warp.

Still another object of the invention is to provide an improved form of blade holding mechanism for holding a doctor blade to a doctor back in which a support plate extends along the front face of the doctor back and is secured thereto and has a uniformly machined blade holding recess with a blade abutment insert recessed therein and extending for the length of the blade for aligning the blade with its clamping plate, in which the clamping plate is clamped to the blade by la series of fluid pressure operated clamping arms and is maintained in true clamping alignment with the blade by an inflatable fluid pressure operated member extending for the length of the clamping plate.

Still another object of the invention is to provide an improved form of retractible guard for a doctor blade, preventing gouging of the back-up roll, and protecting the blade from damage when adjustably moving the blade toward the doctor back and serving as a safety guard, preventing injury that may be caused by brushing along the bare blade.

A still further object of the invention is to provide a novel and improved form of support for the doctor blade and doctor back of a flooded nip coater, in which the limit of movement of the doctor blade toward the back-up roll of the coater is obtained by an improved form of stopping arrangement always stopping the doctor blade in the same relative relation with respect to the back-up roll regardless of variations in load angle of the doctor blade.

These and other objects of the invention will appear from time to time as the following specification proceeds and with reference to the accompanying drawings wherein:

FIGURE 1 is a fragmentary View in side elevation of a flooded nip coater constructed in accordance with the principles of the present invention, with the coating pan partially shown in phantom and the bearing support for the back-up roll broken away;

FIGURE 2 is a viewy in side elevation of a doctor back with the supports and adjusting mechanism therefor \re moved, in order to illustrate the clamping mechanism for y the doctor blade; and

FIGURE 3 is a view somewhat similar to FIGURE Z but showing the clamping means for the doctor blade open and the doctor blade and doctor back in a wash up position.

In the embodiment of the invention illustrated in FIG- URE 1 of the drawings, 10 generally designates a coating device, which comprises a back-up roll or drum 11, partially wrapped by a traveling sheet or web W, and an applicator roll 12 picking up coating material from a coating bath pan 13, partially indicated by dot-dash lines.

The applicator roll 12 picking up coating material from the coating bath pan 13 applies the coating material to the sheet W wrapped beneath and traveling with the backup roll 11 in the nip between said applicator roll and backup roll.

The coating device also includes a doctor blade 15 mounted on and extending along the front face of a doctor back 16, trunnioned on a base 17 on trunnion shafts 1S journalled in trunnion supports 19. The trunnion supports 19 are mounted on and extend upwardly of a support plate 20 mounted on the top of the base 17, for adjustable movement toward and from the axis of the backup roll 11, to vary the angle of the doctor blade 15 with respect to the back-up roll. Adjustment of the support plate 20 along the top surface of the base 17 is attained by operation of an adjustment screw 21 threaded in a nut 22 depending from the support plate. The adjustment means is no part of the present invention so need not herein be shown or described further.

At least one iluid pressure operated cylinder 23 is provided to hold the doctor back in position about the axis of the trunnion shaft 18 and to pivot said doctor back away from the back-up roll 11 into a threading position, and into an extreme retracted clean up position, such as is shown in FIGURE 3.

The cylinder 23 is trunnioned to the base 17 beneath the adjustable support plate 20 on trunnion pins 24 in a conventional manner. The cylinder 23 has a piston (not shown) therein having a piston rod 25 extensible therefrom, having a clevis 26 at its upper end, pivotally connected by a pivot pin 27 to an arm 29 of a bell crank 30. The bell crank 30 is pivoted for movement about an axis coaxial with the axis of the trunnion pins 18. The bell crank 30 has a second upright arm 31 extending upwardly of the pivot thereof in angular forwardly spaced relation with respect to the arm 29 and engageable with an adjustable stop 32 on an arm 33 extending from a bearing bracket 35 for the back-up roll 11 toward the doctor back 16. The adjustable stop 32 may be a micrometer stop to provide a line adjustment of the position of the doctor blade 15 with respect to the face of the back-up roll 11. The adjustable stop 32 being mounted on the bracket or arm 33 extending from the main bearing bracket for the back-up roll 11, Will always be in the same location relative to the back-up roll for all positions of adjustment of the angle of the doctor blade with respect to the back-up roll.

It should be understood that the stop for the doctor back when adjustably moved toward the back-up roll has heretofore been attained by the piston of the positioning cylinder when the piston reaches the end of its travel. This has meant that the length of travel of the piston must be changed each time the doctor back is adjusted toward or from the back-up roll, to change the angle of the doctor blade. The necessity of readjusting the travel of the piston each time the load angle is changed is therefore eliminated by mounting the stop on the bearing for the back-up roll.

The doctor back 16 and doctor blade 15 are loaded by two loading diaphragms 36 and 37 mounted at their outer ends on a plate or pressure pad 39, shown in FIGURE 1 as formed integrally with the arm 29 of the bell crank 30 and mounted on a plate or pressure pad 40 at their opposite ends. The pressure pad `40 is shown as being formed integrally with a loading arm 41 which may be secured to an outer end of the doctor back 16 and which is shown as extending angularly upwardly and rearwardly therefrom.

The diaphragms 36 and 37 are shown in FIGURE 1 as being in the form of air springs of a conventional construction, and may be supplied with air under pressure to delicately load the doctor back 16 `and doctor blade 15 with respect to the Web W, or to accurately space the doctor blade from the web and back-up roll 11, as required in certain coating conditions.

A stop bolt 42 is shown as being threaded in the plate or pressure pad 39 `and as being locked in position by a nut 43. The head of the stop bolt determines the retracted position of the loading arm 41 with respect to the lever arm 29 of the bell crank 30 and prevents complete collapse of the diaphragms 36 and 37.

Referring now in particular to FIGURES 2 and 3, showing the doctor back with its support and loading arms removed in order to more clearly illustrate the invention, and to particularly show the details of the clamping means for clamping the doctor blade 15 to the doctor back 16, a blade supporting plate 45- extends along a front face 46 of the doctor back 16 and faces in the general direction of the back-up roll 11. The blade supporting plate 45 has a substantial surface extending along the front face 46 of the doctor back and is located with respect to the doctor back as by a key 47. The blade Supporting plate 45 is also bolted or otherwise secured to the front face of the doctor back.

The blade supporting plate 45 has a rectangular recess 48 formed therein and opening to the front and top thereof and forming a recess for a holding insert bar 49. The bar 49 forms an abutment bar for the rear face of the blade 15 and may be bolted or otherwise secured l to the blade supporting plate 45. The bar 49 may be machined to the exact size of the recess 48 to cooperate with a clamping plate 50 engageable with the front face of the doctor blade 15 and holding the balde to the blade supporting plate 45. The bar 49 may also be undersized and shimmed to accommodate adjustment of the bar for blades of different thicknesses. Where necessary the bolting means for bolting the bar 49 to the recess 48 may be in the form of jacking screws to jack the bar, to provide a true front abutment face of the bar abutting the blade 15. The recess 48 and holding insert bar 14 being accurately machined, the bar 49 normally provides a true front face engaging the back face of the blade 15, and it ordinarily is not necessary to jack the bar to provide a true blade engaging face, except where warpage of the bar 49 or plate 45 may occur.

The blade supporting plate 45 also has a forwardly stepped recess 51 formed therein providing an abutment and seating recess for the blade 15 and having a lower shoulder 52 against which the bottom of the blade seats. The blade supporting plate 45 also has a forwardly opening rectangular slot 53 extending therealong beneath the blade seating recess 51, for receiving a tongue 55 of the clamping plate 50. The recess 51, shoulder 52, slot 53 and forwardly facing surfaces between said recess and slot are all true and accurately machined surfaces to be interengaged by corresponding trued and accurately machined surfaces on the clamping plate 50, during an operation of clamping the blade 15 in position.

The clamping plate 50 is movably mounted on and eX- tends above the tops of a series of clamping arms 61 spaced along the front face of the doctor back at suitable intervals and is abutted by an inilatable tube 56 recessed within a recess 57 formed in a loading or back-up bar 58, extending for the length of the clamping plate 50. The loading bar 58 is mounted in shouldered recesses 59, of right angled clamping bar holders 60, mounted on and extending upwardly of the tops of the clamping arms 61. The clamping arms 61 and their mountings on the front face of the doctor back are all of the same construction, sollone only need herein be shown and described in deta' The clamping arm 61 is pivoted intermediate its ends in downwardly spaced relation with respect to the clamping plate 50 on a pivot pin 62, mounted in an ear 63, suitably secured to the front face 46 of the doctor back 16 and extending forwardly therefrom. The lower end of the clamping arm 61 is pivotally connected to a connector end 65 of a piston rod 66 on a pivot pin 67. The piston `rod 66 is extensible from a cylinder 69 extending along the bottom lof the doctor back 16 and suitably supported thereon. The cylinder 69 may be an air cylinder and the application of fluid under pressure, such as air, to the -head end thereof will move the clamping arm 61 in a direction to position the clamping plate 50 into clamping engagement with the front face of the blade 15.

It will be noted from FIGURE 3 that the pivot for the clamping arms 61 is spaced a sucient distance beneath the machined surfaces of the supporting plate 45 and the clamping plate 50, to enable said surfaces to be widely separated for washing, to Iaccommodate a thorough Washing of the machined surfaces, and thereby prevent the drying up of coating on the surfaces, which would counteract the close tolerance machining of the machined surfaces of the clamping plate 50 land support plate 45.

It should also be understood that the clamping plate 50, mounted on the upwardly facing surface of the clamp holder 60 for slidable movement therealong towards and from the blade supporting plate 45, when positioned in a clamping position by the clamping arms 61 and held in such a position by the cylinder 69 and piston 66, is moved into tight clamping engagement with the doctor blade by ination of the inflatable tube 56, which may be inflated by air, and which may be bonded to the rear face of the clamping plate 50. The inflatable tube 56, therefore, supplies the pressure to clamp the clamping plate 50 to the blade 15 and to uniformly hold said clamping plate into engagement with the front face of the blade supporting plate 45, and hold the blade true regardless of warpage of the back-up bar 57.

It should also be understood that a plurality of cylinders 69 may be provided to actuate the clamping arms 61, and that an individual cylinder may be provided for each clamping arm under certain operating conditions.

In FIGURE 3, the doctor back is shown as being tilted about the axes of the trunnion pins 18 into a clean up position. In this position of the doctor back, the piston rod 66 may be retracted by the admission of fluid under pressure to the piston rod end of the cylinder 69 to the full extent of its retracted travel, to open the clamping plate 50 with respect to the supporting plate 45 into position to accommodate the free cleaning of coating from the machined surfaces of the supporting plate and clamping plate, at the termination of a coating run, to avoid the collection of coating material on the machine surfaces, as well as on other critical parts of the holding mechanism.

An angular deliector 70 is recessed in a rectangular recess 71 of the clamping plate 50, and extends angularly downwardly of the clamping plate 50 over the back-up bar 58 and beyond the upper ends of the clamping arms 61, to protect the back-up bar and to prevent coating from lodging in the space between the back-up bar 57 and the front face of the clamping plate 50.

A retractible blade guard 73 is pivotally mounted on the top of the doctor back 16. The blade guard 73, as herein shown, comprises a plate 74 supported on spaced arms 75, extending rearwardly therefrom and pivotally mounted on the top of the doctor back 16 on pivot pins 76 extending through ears 77 extending upwardly of the top of the doctor back. The guard plate 74 is shown as having a channel-like rubber tip 78 fitting along the advance edge thereof, to protect persons working around the doctor from injury which may be caused by brushing against the advance edge of the guard and to prevent the guard from gouging the back-up roll 11, when in a safety guarding position. The blade guard 73 is normally in the retracted position shown in FIGURE 2 when the coater is in operation and is moved into its extended position during the threading or wash up operations to protect the doctor blade and also to prevent injury of the operator by the sharp edge of the blade.

While we have herein shown and described one form in which our invention may be embodied, it may readily be understood that various variations and modifications in the invention may be attained without departing from the spirit and scope of the novel concepts thereof.

We claim as our invention:

1. In a doctor for coaters and the like,

a doctor back having a front face,

and a top surface extending rearwardly of said front face,

a doctor blade adapted to be mounted on said doctor back and extending therealong,

a clamping plate clamping said doctor blade to said doctor back,

a series of clamping arms spaced along said doctor back and pivoted to said front face for movement towards and from said doctor blade about coaxial axes spaced downwardly of said blade,

means mounting the clamping plate on said arms for movement thereby into engagement with said doctor blade,

a power means moving said clamping arms toward and from said doctor back and holding said clamping plate in clamping engagement with said doctor blade,

a guard transversely pivoted to said top surface of said doctor back for movement about an axis parallel to the axis of pivotal movement of said clamping arms, and manually positionable over the doctor blade to act as a safety guard for said doctor blade when said clamping plate is released from said doctor blade `during clean up of said clamping plate and doctor blade.

2. In a doctor for coaters and the like,

a doctor back having a front face,

a doctor blade adapted to be mounted on said doctor back to extend along said front face,

means supporting said doctor blade to extend along said front face of said doctor back,

a series of clamping arms spaced along said doctor back in advance of the front face thereof and pivoted for movement toward and from the front face of said doctor back,

a back-up bar extending along said clamping arms,

a clamping plate mounted on said clamping arms for movement toward and from said back-up bar,

fluid pressure cylinder piston means for moving said back-up bar and clamping plate toward the front face of the doctor back and maintaining said clamping plate in clamping engagement with the doctor blade,

and an inatable tube extending along said back-up bar and engaging said clamping plate, and maintaining a uniform clamping pressure thereon throughout the length thereof.

3. In a doctor for coaters and the like,

a doctor back having a front face,

a Idoctor blade extending along said front face of said doctor back,

means clamping said do-ctor blade to said doctor back comprising a blade supporting plate secured to and extending along the front face of said doctor back and having a doctor blade seating recess extending therealong,

a clamping plate for clamping said doctor blade to said recess,

spaced clamping arms supporting said clamping plate for movement into and out of clamping engagement with said doctor blade,

coaxial pivotal mountings for said clamping arms, spaced downwardly along said front face of said doctor back a substantial distance beneath said blade seating recess, to accommodate wide separation between said clamping plate and said doctor blade,

power means for moving said clamping arms to move said clamping plate into and out of clamping engagement with said doctor blade,

and power means interposed between said arms and clamping plate comprising an inflatable tube, inatable to maintain a uniform clamping pressure on said clamping plate for the length of the doctor blade.

4. In a doctor for coaters and the like,

a doctor back having a front face,

a doctor blade adapted to extend along said front face of said doctor back in advance thereof and upwardly therealong,

a blade supporting plate secured to and extending along the front face of said doctor back and having a doctor blade seating recess extending therealong,

a clamping plate engageable with the front face of said doctor blade,

spaced clamping arms supporting said clamping plate for movement into and out of clamping engagement with said doctor blade,

coaxial pivotal mountings for said clamping arms,

spaced downwardly along said front face a substantial distance beneath said blade seating recess of said support plate,

a back-up bar mounted on said clamping arms and extending therealong,

said clamping plate extending along said back-up bar and moved thereby into engagement with said support plate and said doctor blade seated thereon upon movement of said clamping arms toward said support plate,

uid pressure operated cylinder and piston means for moving said clamping arms toward and from said support plate and for holding said clamping arms in position with respect to said blade supporting plate,

and an inflatable tube extending along said back-up bar and engaging said clamping plate, said tube being inflatable to exert a uniform pressure on said clamping plate throughout the length thereof, to uniformly clamp the doctor blade to said blade seating recess.

5. In a doctor and in combination with a back-up roll for coaters and the like,

a doctor back having a front face facing generally in the direction of the back-up roll, and mounted for movement toward and from said back-up roll about an axis parallel to the axis of rotation of said roll and spaced therefrom,

fluid pressure means for moving said doctor back into doctoring cooperation with said back-up roll and retracting said doctor back into a washup position,

a doctor blade adapted to extend along said doctor back and be positioned thereby in doctoring cooperation with said back-up roll,

means clamping said doctor blade to said doctor back comprising a blade supporting plate secured to and extending along the front face of said doctor back and upwardly therefrom and having a doctor blade seating recess extending therealong,

a plurality of parallel spaced clamping arms pivotally mounted on said front face of said doctor back in downwardly spaced relation with respect to said blade receiving recess,

uid pressure operated means for pivotally moving said clamping arms tow-ard and from said blade supporting plate,

a back-up bar supported -on said arms and extending upwardly therefrom,

a clamping plate movably mounted on said arms and backed up by said back-up bar and moved by said arms toward said blade supporting plate into a clamping position, and separated from said blade support- 8 ing plate by said arms into a widely open clean up position, and an inflatable tube recessed in said backup plate and having engagement with said clamping plate for the length thereof, for exerting a uniform clamping pressure on said clamping plate and the blade seated in said blade supporting plate upon the supply of fluid under pressure to said inflatable tube.

6. In a doctor and in combination with a back-up roll for coaters and the like,

a doctor back having a front face facing in the general direction of the back-up roll and pivotally mounted for movement toward land from the back-up roll,

means holding said doctor back in position and moving said doctor back toward and from the back-up roll,

a blade supporting plate extending along the front face of said doctor back and rigidly secured thereto,

said blade supporting plate having a forwardly and upwardly -opening machine finished blade seating recess extending therealong,

a doctor blade seated in said recess,

a clamping plate,

a plurality of parallel spaced clamping arms pivotally mounted on said doctor back in advance of the front face thereof and having upper support ends, a back-up bar mounted on said clamping arms and extending along said clamping plate,

fluid pressure operated means for moving said clamping arms, back-up bar and clamping plate toward and from said blade supporting plate,

said clamping plate having a face machine finished to accurately conform to said recess and the machine nished front face of said blade supporting plate and the blade seated in said recess, and movable into said recess by operation of said clamping arms into clamping engagement with -a doctor blade seated in said recess, and power means between said back-up bar and clamping plate for exerting uniform clamping pressure on said clamping plate throughout the length thereof.

'7. A doctor in accordance with claim 6 wherein the blade supporting plate has an upwardly and forwardly opening recess therein stepped rearwardly of the seating recess for said doctor blade and wherein a removable insert bar is mounted in said upwardly and forwardly opening recess and forms a clamping abutment surface for the rear face of said doctor blade,

8. A doctor in accord-ance with claim 6 wherein the blade supporting plate has a recess extending therealong opening to said first mentioned recess and to the top of said support plate,

wherein a removable clamping insert bar is mounted in said recess and forms a clamping abutment surface for the rear face of the doctor blade,

wherein the back-up plate has a recess therein opening to said clamping plate,

and wherein the power means comprises an inflatable tube extending along said recess into engagement with an adjacent face of said clamping plate for exerting uniform clamping pressure on said clamping plate throughout the length thereof.

9. A doctor for web coaters and the like comprising,

a doctor back pivotally mounted for cooperative movement toward and from a back-up roll of the web coater,

said doctor back having a front face facing in the general direction of the back-up roll and having a blade supporting plate extending along the front face of said doctor back and upwardly therefrom,

keying means locating said blade supporting plate with respect to said doctor back,

other means rigidly securing said vblade supporting plate to said doctor back,

said blade supporting plate having a machine finished recess extending for the length thereof opening to the top and front of said plate, and forming a doctor blade seating recess and having a removable insert bar recessed. in and extending along the top thereof and having a front face in general alignment with a front face of said blade seating recess,

said blade supporting plate also having a downwardly spaced machine finished slot extending therealong, opening to said front wall,

a plurality of clamping arms transversely pivoted to the front face of said doctor back in downwardly spaced relation with respect to said support plate,

fluid pressure operated means for moving said clamping arms toward and from said support plate,

and a clamping plate carried by said clamping arms and extending upwardly therefrom and having a machine finished face generally confor-ming -to the machine finished face of said support plate and including a tongue extending therefrom fitting within said slot in said support plate and assuring uniform clamping of a doctor blade to said blade seating recess.

10. A doctor in accordance with claim 9,

wherein the clamping plate is movably mounted on said clamping arms for movement toward and 'from said support plate,

wherein a backing plate backs up said clamping plate,

and wherein an inatable tube carried by said backing plate has engagement with an adjacent face of said clamping plate for the length thereof, for exerting a uniform pressure on said clamping plate to effect uniform clamping of the doctor blade to said insert for the length thereof.

11. A doctor in accordance with claim 9,

wherein a retractible guard is transversely pivoted to the top surface of said doctor and extends for the length thereof and is positionable to extend over said `doctor blade during a web threading and cleaning operation and is retractible to be free from said` doctor blade during a coating operation. 12. In a device for coating a traveling web of paper,

in combination:

a back-up roll wrapped by a traveling web,

an applicator roll in nip defining relation with respect to said back-up roll applying coating to a web passing in the spa-ce between said rolls,

a stationary bearing support for said back-up roll,

a doctor blade on the outgoing side of said back-up roll,

a doctor 4back supporting said doctor blade and operable to move said doctor blade toward and from said back up roll and to vary the angle of said doctor -blade with respect to said back-up roll,

spaced trunnion supports for supporting said doctor back for adjustable movement about an axis parallel to the axis of rotation of said back-up roll,

tluid pressure means for moving said doctor blade and doctor back toward and from said back-up roll,

other means adjusting the position of said doctor back -with respect to said back-np roll and varying the angle of the doctor Iblade with respect to said back-up roll,

and stop means mounted on and extending from said bearing support for said back-up roll toward said doctor back and limiting movement of said doctor back and doctor blade toward said back-up roll,

said stop means always being in the same position relative to said back-up roll regardless of the position of adjustment of said doctor back and blade with respect to said back-up roll, to change the blade angle of said doctor blade.

13. A coating device in accordance with claim 12,

wherein the doctor yback is rectilinearly adjustable toward and from the back-up roll to vary the angle of the doctor blade with respect to the periphery vof the back-up roll,

and wherein uid pressure operated loading means are provided to load said doctor blade with respect to said back-up roll.

14. A doctor in accordance with claim 12,

wherein the means for moving the doctor back a-nd blade toward and from the back-up roll about the u axis of pivotal movement of said doctor back comprises,

at least one uid pressure operated cylinder and piston,

a bell crank pivoted for movement about an axis coaxial with the axis of pivotal movement of the doctor back,

an operative connection from said cylinder and piston to one arm of said bell crank,

lluid pressure operated diaphragms interposed between said one arm of said bell crank and said doctor back for loading said doctor blade,

wherein the doctor back is mounted for rectilinear fmovement in a horizontal plane toward and from the back-up roll to vary the angle of the doctor blade with respect to said back-up roll,

wherein the stop means comprises a stop arm mounted on the bearing support for said back-up roll and extending toward said doctor back and having a stop on the end thereof facing said doctor back,

and wherein the bell crank has a second upright arm engageable with said stop and limiting movement of said bell crank and doctor kback toward said back-up roll.

15. In a doctor for coaters and the like,

a doctor back having a front face,

a doctor blade extending along said front face of said doctor back,

means clamping said doctor blade to said doctor back comprising a blade supporting plate secured to and extending along the front face of said doctor back and having a doctor blade seating recess extending therealong,

a clamping plate for clamping said doctor blade to said recess,

spaced clamping arms supporting said clamping plate for movement into and out of clamping engagement with said doctor blade,

coaxial pivotal -mountings for said clamping arms, spaced downwardly along saidfront face of said doctor back a substantial distance beneath said blade seating recess, to accommodate wide separation between said clamping plate and said doctor blade,

fluid pressure operated cylinder and piston means connected between said doctor back and clamping arms `for moving said clamping plate into and out of clamping engagement with said doctor blade and for holding said clamping plate into engagement with said doctor blade,

and pressure means interposed between said clamping arms and said clamping plate and operable to maintain a uniform clamping pressure on said clamping plate for the length of said doctor blade.

References Cited UNITED STATES PATENTS 3,006,275 10/ 1961 Allen. 3,138,207 4/ 1964 Schmitt 118-26 3,245,378 4/1966 Caple et al. 118-126 3,255,038 6/1966 Coghill 118-126 X FOREIGN PATENTS 63 8,880 3/1962 Canada.

CHARLES A. WILLMUTH, Primary Examiner.

R. I. SMITH, Assistant Examiner. 

1. IN A DOCTOR FOR COATERS AND THE LIKE, A DOCTOR BACK HAVING A FRONT FACE, AND A TOP SURFACE EXTENDING REARWARDLY OF SAID FRONT FACE, A DOCTOR BLADE ADAPTED TO BE MOUNTED ON SAID DOCTOR BACK AND EXTENDING THEREALONG, A CLAMPING PLATE CLAMPING SAID DOCTOR BLADE TO SAID DOCTOR BACK, A SERIES OF CLAMPING ARMS SPACED ALONG SAID DOCTOR BACK AND PIVOTED TO SAID FRONT FACE FOR MOVEMENT TOWARDS AND FROM SAID DOCTOR BLADE ABOUT COAXIAL AXES SPACED DOWNWARDLY OF SAID BLADE, MEANS MOUNTING THE CLAMPING PLATE ON SAID ARMS FOR MOVEMENT THEREBY INTO ENGAGEMENT WITH SAID DOCTOR BLADE, A POWER MEANS MOVING SAID CLAMPING ARMS TOWARD AND FROM SAID DOCTOR BACK AND HOLDING SAID CLAMPING PLATE IN CLAMPING ENGAGEMENT WITH SAID DOCTOR BLADE, A GUARD TRANVERSELY PIVOTED TO SAID TOP SURFACE OF SAID DOCTOR BACK FOR MOVEMENT ABOUT AN AXIS PARALLEL TO THE AXIS OF PIVOTAL MOVEMENT OF SAID CLAMPING ARMS, AND MANUALLY POSITIONABLE OVER THE DOCTOR BLADE TO ACT AS A SAFETY GUARD FOR SAID DOCTOR BLADE WHEN SAID CLAMPING PLATE IS RELEASED FROM SAID DOCTOR BLADE DURING CLEAN UP OF SAID CLAMPING PLATE AND DOCTOR BLADE. 